Twelve people were killed and three injured when a truck crashed into a coach in the mountainous northern Vietnamese province of Lai Chau on Saturday, Xinhua reported, citing the provincial police.

The accident occurred at around 9:30 a.m. local time on National Highway 4D in Tam Duong district. The truck hit the back of the coach while driving down a pass, according to the Vietnam News Agency.

Both vehicles dropped off the bridge into the river after the collision.

An investigation into the cause of the accident is underway.